The present invention is directed to water-sensitive compositions having improved processability. In addition, the present invention is directed to a process of making water-dispersible thermoformable articles, such as fibers, films and fabrics, which maintain their integrity and strength when in use, but dissolve and disperse when placed in contact with large amounts of water, such as in a conventional toilet. Moreover, the present invention is directed to water-dispersible products, including flushable products such as personal care products, diapers, feminine napkins, wipes, incontinence products, release liners, product packaging, etc., which contain the above-mentioned fibers, films and fabrics.
Disposable products have revolutionized modern lifestyle and are of great convenience to society. Such products generally are relatively inexpensive, sanitary and quick and easy to use. Disposal of such products, however, is a concern as landfills close and incineration contributes to urban smog and pollution. Consequently, there is an urgent need for disposable products that can be disposed of without dumping or incineration. An ideal disposal alternative would be the use of municipal sewage treatment plants and private residential septic systems. Products suited for disposal in sewage systems that can be flushed down a conventional toilet are termed xe2x80x9cflushable.xe2x80x9d An essential feature of flushable products is that they must have sufficient wet strength for their intended use, yet lose structural integrity upon contact with water.
Numerous attempts have been made to produce flushable fibers, fabrics, films and adhesives that retain their integrity and wet strength during use, yet can be disposed of via flushing in conventional toilets. One approach to producing a flushable product is to limit the size of the product so that it will readily pass through plumbing without causing obstructions or blockages. Such products have high wet strength, yet do not disintegrate during flushing. Examples of this type of. product include wipes such as baby wipes. This approach to flushability suffers the disadvantage, however, of being restricted to small sized articles. Many of the current flushable products are limited to such small articles.
Another approach to producing a flushable product is to manufacture a product that is normally insoluble in water, but which disintegrates in the presence of alkaline or acidic aqueous solutions. The end user is provided with an alkaline or acidic material to add to the water in which the product is to be disposed. This approach permits disposal via normal plumbing systems of products substantially larger than wipes, but suffers from the disadvantage of forcing the user to perform the step of adding the dissolving chemical to the water. A further disadvantage is that the inadvertent or unintentional disposal of such a product in a conventional toilet without the addition of the dissolving chemical can cause serious obstruction or blockage of the plumbing system. The latter disadvantage can, however, be overcome by incorporating the dissolving acid or alkali into the article but separate from the dissolvable material while in use. The dissolving chemical is only released upon contact with water during flushing.
Another approach to producing a flushable product is to prepare products such as fibers, fabrics and films from water soluble materials. Upon contact with water, the water soluble material dissolves, reducing the structural integrity of the product, and causing its disintegration, such that it will easily pass through the plumbing system. Although the products prepared by this approach are suitable for dry applications wherein the product does not come in contact with any aqueous solution, these products are not suited for applications, such as personal care products, wherein the product may come into contact with even a relatively small amount of aqueous solution.
One approach to producing thermoformable articles for use in personal care products, which can withstand prolonged contact with body fluids, such as blood, urine, and perspiration, has been the use of xe2x80x9cion triggerablexe2x80x9d polymeric materials. Such xe2x80x9cion triggerablexe2x80x9d polymeric materials remain stable when in contact with aqueous solutions having a relatively high ion concentration, but dissolve and disperse when placed in contact with aqueous solutions having a relatively low ion concentration, such as ordinary tap water. In other words, the polymeric materials possess xe2x80x9cwater triggerability.xe2x80x9d Ion triggerable polymeric materials have been used as binders for nonwoven webs and also as a thermoformable material. For example, a salt sensitive water soluble polyurethane binder for flushable nonwoven fabrics is disclosed in U.S. Pat. No. 4,002,171, issued to Taft. Further, a salt sensitive water soluble terpolymer for making flushable paper diapers, bandages and sanitary towels is disclosed in Japanese Patent No. JP 5125123 and U.S. Pat. No. 5,312,883 assigned to LION Corp.
A more recent approach to forming ion triggerable articles is described in U.S. patent application Ser. No. 08/730,951, assigned to Kimberly-Clark Worldwide, the assignee of the present invention. In U.S. patent application Ser. No. 08/730,951, thermoformable articles are prepared from ion triggerable materials. A preferred ion triggerable material, a copolyester which dissolves and disperses in tap water in no more than 60 minutes, offers good water responsiveness. However, the copolyester exhibits processability constraints. Typically, the copolyester has poor melt strength, is very sticky, and is very difficult to stretch into a fine fiber without breaking. Past efforts have been made to try to improve the processability of the copolyester, but have failed. The resulting fibers possess a melt strength that is not high enough to ensure good fiber processing into a desirable denier range (less than 7 denier per fiber). In addition, silicone oil based finishing agents were required to avoid the stickiness of the resulting fibers, which can affect adhesion properties of binder fibers.
What is needed in the art is a method of improving the processability of existing water-sensitive polymeric materials.
Also, what is needed in the art is water-sensitive thermoformable articles having improved processability wherein the articles maintain structural integrity when exposed to ionic aqueous solutions, such as body fluids, yet readily disperse when flushed down a conventional toilet. Further, what is needed in the art is personal care products comprising thermoformable articles having improved processability wherein the personal care products maintain structural integrity when exposed to body fluids, such as blood, urine, perspiration, and other body fluids, yet readily disperse when flushed down a conventional toilet.
The present invention is directed to unique compositions which provide significantly improved processability.
The compositions comprise a blend of at least one water-sensitive polymer and at least one polymer selected from polylactide (PLA), polyolefin-grafted with one or more polar groups, such as maleic anhydride (MA), and other aliphatic polyesters. Desirably, the water-sensitive polymer comprises one or more copolyesters. The compositions may be spun into monocomponent or multicomponent fibers through conventional processes, such as spunbonding and meltblowing processes. The compositions may also be extruded to form films and other thermoformable articles.
The present invention is also directed to multicomponent fibers, such as sheath/core fibers, wherein the compositions described above are present on an outer surface of the multicomponent fiber. In sheath/core multicomponent fiber applications, the composition in the sheath structure has xe2x80x9cion triggerabilityxe2x80x9d which allows water to dissolve the sheath material, while the core materials are polymeric materials, such as polyolefins, which provide processing and binding strength and reduce the fiber cost. Other heteromorphic multicomponent fiber configurations suitable for the present invention include, but are not limited to, side-by-side, pie-shape, and island-in-the-sea fiber configurations. The resulting fibers may be used to form air-laid nonwovens for use as coverstock, liners or absorbent webs in a variety of products including, but not limited to, personal care products.
The compositions of the present invention may also be used as a coating or co-extruded component of a flushable film for applications in composite cloth-like outercover for flushable diapers, or as a baffle barrier film for feminine care napkins and adult incontinence products. The present invention has broad applicability for any single use flushable product requiring a barrier film, spun fiber, absorbent core, or any combination thereof.
The present invention overcomes the previously mentioned processability problems associated with the production of thermoformable articles comprising water-sensitive polymers. The compositions of the present invention not only significantly improve processability, but also maintain water triggerability. In the case of fibers, the improved processability is evidenced by a maximum jet stretching ratio and a reduction in fiber stickiness. In general, the compositions of the present invention comprise at least one water-sensitive polymer, desirably a copolyester, and at least one additional polymer selected from polylactide (PLA), polyolefin-grafted with one or more polar groups, such as maleic anhydride (MA), and other aliphatic polyesters.
Suitable water-sensitive polymers for the compositions of the present invention include polymers which remain stable when in contact with aqueous solutions having a relatively high ion concentration, but dissolve and disperse when placed in contact with aqueous solutions having a relatively low ion concentration, such as ordinary tap water. Typically, the polymer contains one or more ion sensitive functional group, such as sulfonate and carboxylate groups. Polymers for use in the present invention include, but are not limited to, copolyesters available from National Starch and Chemical Company under the product designations NS 70-4395 and NS 70-4442; copolyesters available from Eastman Chemical Company (Kingsport, Tenn.) under the product designations AQ29S, AQ38S, AQ55S, AQ1350 and AQ1950; and copolymers and terpolymers of acrylic acids and/or acrylate esters, such as those available from Lion Corporation (Tokyo, Japan) or Belland (Switzerland). Particularly suitable polymers include the NS 70-4395 and NS 70-4442 copolyesters available from National Starch and Chemical Company.
The compositions of the present invention also contain at least one additional polymer selected from polylactide (PLA), polyolefin-grafted with one or more polar groups, such as maleic anhydride (MA), and other aliphatic polyesters. As used herein, the term xe2x80x9cpolylactidexe2x80x9d includes the polylactide polymer and copolymers thereof, such as a copolymer of optical isomers of lactide or copolymers such as lactide and caprolactone copolymers. Suitable polyolefins to be grafted with one or more polar groups include, but are not limited to, polyethylene, polypropylene, ethylene-propylene copolymers, and polybutylene. Suitable polar groups for grafting onto the polyolefin polymer chain include, but are not limited to, maleic anhydride (MA), polyethylene glycol (PEG), polyethylene glycol methacrylate (PEGMA), hydroxyethyl methacrylate (HEMA), 2-ethylhexyl methacrylate (EHMA), vinyl alcohol, vinyl acetate, and other polar groups. Suitable other aliphatic polyesters include, but are not limited to, polybutylene succinate, polybutylene succinate-co-adipate, polycaprolactone, SKYGREEN(trademark) (See U.S. Pat. No. 5,470,941; assigned to Sunkyoung Industries), and blends of the above-mentioned polymers. Desirably, the at least one additional polymer component is a polyester having good compatibility with the water-sensitive polymer. More desirably, the at least one additional polymer component is a polylactide copolymer having a similar melt viscosity to the water-sensitive polymer.
The weight ratio of the water-sensitive polymer to the polylactide (PLA), polyolefin-grafted with one or more polar groups, or other aliphatic polyesters, may vary greatly; however, certain applications, such as fine fibers, may require a particular weight ratio. Desirably, the weight ratio of water-sensitive polymer to the at least one additional polymer component is from about 60:40 to about 90:10. More desirably, the weight ratio of copolyester to the at least one additional polymer component is from about 70:30 to about 90:10. More desirably, the weight ratio of water-sensitive polymer to the at least one additional polymer component is from about 75:25 to about 85:15. When the weight ratio of water-sensitive polymer to the at least one additional polymer component is less than about 60:40, the composition exhibits less than desirable ion triggerability and flushability for personal care products. When the weight ratio of water-sensitive polymer to the at least one additional polymer component is greater than about 90:10, the composition exhibits potential processability difficulty, especially in the case of the composition being spun into fine fibers. Table 1 below lists the properties of various fibers comprising compositions of the present invention and unmodified fibers (i.e., fibers comprising a copolyester without processability-enhancing additives).
The water-sensitive composition of the present invention may be thermoformed into a variety of articles including, but not limited to, fibers, fabrics, films and absorbents. The water-sensitive composition can be spun into monocomponent fibers or multicomponent fibers. As used herein, the term xe2x80x9cmonocomponent fiberxe2x80x9d means a fiber formed solely from the water-sensitive composition of the present invention. As used herein, the term xe2x80x9cmulticomponent fiberxe2x80x9d means a fiber formed from the water-sensitive composition of the present invention and at least one other material. The water-sensitive fibers may be formed using any conventional fiber forming process including, but not limited to, meltblowing and spunbonding processes. The fibers may be continuous or discontinuous. Continuous fibers may be formed by any spinning operation. Continuous fibers may be cut to form discontinuous fibers having suitable lengths for nonwoven processes such as carding (approximate length of 25 to 45 mm) or air-laying (approximate length of 0.2 to 15 mm).
In one embodiment of the present invention, the water-sensitive composition may be thermoformed into multicomponent fibers, such as sheath/core fibers, wherein the water-sensitive compositions described above are present on at least a portion of the outer surface of the multicomponent fiber. Desirably, the multicomponent fibers are bicomponent fibers wherein the water-sensitive composition of the present invention occupies at least a portion of the outer surface of the fiber and at least one additional material occupies the remainder of the fiber. More desirably, the bicomponent fiber has a sheath/core structure wherein the water-sensitive composition of the present invention forms the sheath, and a second material, such as a polymer having a melting temperature about 20xc2x0 C. or greater than the melting temperature of the sheath material, forms the core. Most desirably, the bicomponent fiber has a sheath/core structure wherein the water-sensitive composition of the present invention forms the sheath, and the core material is polypropylene (PP), polyethylene (PE), or a combination thereof. In sheath/core multicomponent fiber applications, the composition in the sheath structure has xe2x80x9cion triggerabilityxe2x80x9d which allows water to dissolve the sheath material, while the core materials are polymeric materials, such as polyolefins, which provide improved processing and binding strength and reduce the fiber cost. Although a concentric sheath/core fiber structure is a desirable embodiment, any other heteromorphic fiber configuration may be used including, but not limited to, pie shape, side-by-side, and island-in-the-sea etc., to achieve different degrees of triggerability, mechanical and tactile properties depending on the end use of the water-sensitive fibers. For flushable fiber applications, desirably the water-sensitive composition represents a continuous phase through the fiber so that the fiber disperses when placed in a conventional toilet.
The water-sensitive fibers of the present invention may be used alone or combined with other fibrous materials to form nonwoven, as well as, woven fabrics. In one embodiment of the present invention, the water-sensitive fibers of the present invention are useful as binder fibers alone or in combination with other fibrous material to form a nonwoven web. Other fibrous materials for use with the water-sensitive fibers of the present invention include natural fibers, synthetic fibers, and combinations thereof. The choice of fibers depends upon, for example, fiber cost and the intended end use of the finished fabric. For instance, suitable fabrics may include the water-sensitive fibers of the present invention and natural fibers including, but not limited to, cotton, linen, jute, hemp, wool, and wood pulp. Similarly, regenerated cellulosic fibers such as viscose rayon and cuprammonium rayon, modified cellulosic fibers, such as cellulose acetate, or synthetic fibers such as those derived from polyvinyl alcohol, polyesters, polyamides, polyacrylics, etc., alone or in combination with one another, may likewise be used in combination with the water-sensitive fibers of the present invention.
Depending on the end use of the finished fabric, the fiber length may be important in producing the fabrics of the present invention. In some embodiments such as flushable products, fiber length is of more importance. The minimum length of the fibers depends on the method selected for forming the fibrous substrate. For example, where the fibrous substrate is formed by carding, the length of the fiber should usually be at least about 30 mm in order to insure uniformity. Where the fibrous substrate is formed by air-laid or wet-laid processes, the fiber length may desirably be about 0.2 to 15 mm, more desirably about 0.2 to 6 mm. Although fibers having a length of greater than 50 mm are within the scope of the present invention, it has been determined that when a substantial quantity of fibers having a length greater than about 15 mm is placed in a flushable fabric, though the fibers will disperse and separate in water, their length tends to form xe2x80x9cropesxe2x80x9d of fibers which can become entangled in home lateral piping obstructions, such as tree roots or bends in the piping. Therefore, for these products, it is desired that the fiber length be about 15 mm or less so that the fibers will not have a tendency to xe2x80x9cropexe2x80x9d when they are flushed through a toilet. Although fibers of various length are applicable in the present invention, desirably fibers are of a length less than about 15 mm so that the fibers separate easily from one another when in contact with water, most desirably ranging from about 0.2 mm to about 6 mm in length.
Nonwoven fabrics containing the water-sensitive fibers of the present invention may be formed from a single layer or multiple layers. In the case of multiple layers, the layers are generally positioned in a juxtaposed or surface-to-surface relationship and all or a portion of the layers may be bound to adjacent layers. The nonwoven fabrics may also be formed from a plurality of separate nonwoven webs wherein the separate nonwoven webs may be formed from single or multiple layers. In those instances where the nonwoven web includes multiple layers, one or more of the multiple layers may contain water-sensitive fibers of the present invention.
The water-sensitive fibers of the present invention, alone or in combination with one or more additional fibers, are particularly useful for forming air-laid nonwoven fabrics. Air-laid fabrics find particularly useful application as body-side liners, fluid distribution materials, fluid in-take materials (surge), cover stock and absorbent structures for various water-dispersible personal care products. The basis weights for these air-laid nonwoven fabrics will usually range from about 10 to about 200 gram per square meter (gsm). Short fibers of length less than about 15 mm are desirably used to make these flushable products. Surge or in-take materials need better resiliency and higher loft so at least some of the fibers in these air-laid nonwoven fabrics have a fiber titre of about 3 denier (d) or greater, more desirably about 6 denier (d) or greater. A desirable final density for the surge or in-take materials is between about 0.025 and about 0.050 grams per cubic centimeter (g/cc). Fluid distribution materials will have a higher density, in the desired range of about 0.10 to about 0.20 g/cc using at least some fibers of lower denier, most desirably, at least some fibers having a denier of about 3 d or less.
The water-sensitive compositions of the present invention may also be used in cast film and/or blown film applications. Films formed from the water-sensitive compositions of the present invention may be made entirely of the water-sensitive composition of the present invention or may contain the water-sensitive composition, as well as, other polymeric materials. Additionally, films may also be made by mixing various water-sensitive compositions. Desirably, the resulting film will contain a continuous phase of one or more water-sensitive compositions so that the film will disperse when placed in contact with water. Desirably, films formed from the water-sensitive composition of the present invention comprise at least 50 vol % of the water-sensitive composition of the present invention. More desirably, films formed from the water-sensitive composition of the present invention comprise from about 50 to about 90 vol % of the water-sensitive composition of the present invention. Most desirably, films formed from the water-sensitive composition of the present invention comprise from about 70 to about 90 vol % of the water-sensitive composition of the present invention.
The thickness of the film may vary greatly depending upon the end use of the film-containing product. Film thickness should be minimized when possible to reduce product cost and to reduce the time necessary for the film to disperse, especially in the case of flushable products. Desirably, the film thickness will be less than about 2.0 mil (50.8 micrometers). More desirably, the water-soluble film thickness will be from about 0.1 mil (2.54 micrometers) to about 1.0 mil (25.4 micrometers). Most desirably, the water-soluble film thickness will be from about 0.3 mil (7.62 micrometers) to about 1.0 mil (25.4 micrometers).
In one embodiment of the present invention, films formed from the water-sensitive composition of the present invention may be combined with one or more additional polymer films to impart specific mechanical, biodegradable, barrier and/or tactile properties to the film combination. Desirably, at least one film formed from the water-sensitive composition of the present invention is co-extruded with one or more additional polymer films to form a composite film.
In some embodiments, it may be desirable to incorporate one or more additives into the water-sensitive. composition of the present invention. One or more additives may be added to the water-sensitive composition of the present invention to aid in the melt-processing applications described above. It should be noted that although fibers and films are desirable products formed from the water-sensitive composition of the present invention, other articles of manufacture may also be produced from the water-sensitive composition of the present invention. Such articles include, but are not limited to, compression molded articles, blow molded articles, injection molded articles, foam sheets and coated articles. Additives may be used in any of the above-mentioned articles. Further, additives may be used to provide one or more desired properties to articles formed from the water-sensitive composition of the present invention. Suitable additives include, but are not limited to, compatibilizers, processing aids, dispersants, slip agents, thickening agents, anti-foaming agents, and anti-microbial agents, antioxidants, as fabricating agents or as modifiers depending on the specific properties desired in the final product.
The fabrics and films of the present invention may be incorporated into such body fluid absorbent products as sanitary napkins, diapers, surgical dressings, tissues, wet wipes, incontinence devices and the like. These products may include an absorbent core, comprising one or more layers of an absorbent fibrous material. The core may also comprise one or more layers of a fluid-pervious element, such as fibrous tissue, gauze, plastic netting, etc. These are generally useful as wrapping materials to hold the components of the core together. Additionally, the core may comprise a fluid-impervious element or barrier means to preclude the passage of fluid through the core and on the outer surfaces of the product. Preferably, the barrier means also is water-dispersible. A film of a polymer having substantially the same composition as the aforesaid water-sensitive composition is particularly well-suited for this purpose. In accordance with the present invention, the polymer compositions are useful for forming each of the above-mentioned product components including the layers of absorbent core, the fluid-pervious element, the wrapping materials, and the fluid-impervious element or barrier means.
Those skilled in the art will readily understand that the water-sensitive compositions of the present invention may be advantageously employed in the preparation of a wide variety of products designed to withstand contact with salt solutions, yet disperse in large amounts of water. Such products may only comprise a single layer of the water-sensitive composition in the form of a layer of fibers, a film or a fabric, or may comprise the water-sensitive composition in the form of a layer of fibers, a film or a fabric in combination with one or more additional layers such as coatings, films, fabrics, etc. Although the water-sensitive composition and articles formed therefrom of the present invention are particularly suited for personal care products, the water-sensitive composition and articles formed therefrom of the present invention may be advantageously employed in the preparation of a wide variety of consumer products other than personal care products.